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Liquid metal reactors (LMRs) involved both sodium fast reactors (SFRs) and lead fast reactors (LFRs) have gained great development over the world due to their nuclear fuel breeding and nuclear waste transmutation capability. For the purpose of meeting the design and construction requirements of LMRs in China, a subchannel program FLARE based on the MOOSE framework for LMRs was developed. The program considers four conservation equations: mass, momentum, and energy in the axial direction, along with momentum in the transverse direction. Additionally, a hybrid approach that integrates the discontinuous Galerkin (DG) and finite element method (FEM) for discretizing conservation equations was employed in FLARE PROGRAM. Advanced closure models such as pressure drop, heat transfer, and material properties of sodium, lead bismuth, and lead were incorporated. In detail, the program integrates the Upgraded Cheng and Todreas (UCTD) wall friction model, Cheng and Todreas (CT) turbulence mixing model, CT transverse heat conduction model, along with some heat transfer correlations with a wide applicability range, while considering geometric effects and flow conditions. To solve the coupled nonlinear partial differential equations, the Jacobians-Free Newton-Krylov (JFNK) algorithm was used. To validate the accuracy of the constitutive models for swirling flow effect implemented in FLARE program, Toshiba 37-pin was computationally simulated, and the results from FLARE PROGRAM were compared with experimental data as well as results from similar programs. The results demonstrate that the computational results from the FLARE program exhibit good agreement with experimental data as well as calculations from similar programs. The maximum error at high and medium flow rates is 12.6% of the inlet-outlet temperature difference, while the error remains within 10% at low flow rates. Moreover, the correctness of the transverse heat conduction correction model was validated through low-flow conditions. To further validate the computational capability of the FLARE program, the KNS 37-pin experiment was selected for simulation. FLARE program exhibits a maximum error of 6.3% in the radial distribution calculation of coolant channel temperature and 8.51% in the axial distribution, demonstrating good overall agreement with experimental values and high computational accuracy. Finally, to validate the FLARE program’s capability for thermal-hydraulic safety analysis of the reactor core, analysis and calculations were performed on the hottest component of the ALFRED conceptual design reactor. Due to the lack of directly comparable experimental data, the results of FLARE program were validated through comparison with those obtained from the similar program SACOS-LMR. The results show that FLARE program provides reasonable calculations for the axial temperature distribution of the hottest fuel rod cladding and core block, and shows good agreement with SACOS-LMR program. This confirms FLARE program’s capability for accurately calculating the temperature distribution of reactor coolant and fuel rods within the core.

Against the backdrop of China's ambitious three-step nuclear energy development strategy, encompassing pressurized water reactors (PWR), fast reactors (FR), and fusion reactors (FNR), the purpose of this study is to meet the pivotal need for a specialized sub-channel analysis code tailored to the unique thermal-hydraulic characteristics of liquid metal fast reactors (LMFRs). Building upon the foundational SACOS sub-channel code, the approach involves the seamless integration of LMFR-specific models. These include the wire-wrapped model, turbulent crossflow model, and liquid metal convective heat exchange model. The utilization of advanced computational techniques, such as the SIMPLE algorithm and staggered grid methodology, ensures the completion of accurate sub-channel calculations, establishing SACOS-LMR as a robust code for thermal-hydraulic safety analysis in LMFRs. Validation of the SACOS-LMR code was conducted through a sodium transient experiment involving 37-pin bundles at the Karlsruhe Institute of Technology. The results not only demonstrate a commendable alignment between computed parameters (e.g. temperature distribution, pressure drop) and experimental values but also confirm the code's precision in transient analysis for LMFRs. Applying the validated SACOS-LMR code, an in-depth thermal-hydraulic safety analysis of the European Lead-cooled Fast Reactor (ALFRED) core was conducted. The calculated results are not only reasonable but also exhibit consistency with comparable codes, affirming SACOS-LMR's applicability for LMFR core design and thermal-hydraulic analysis. In conclusion, this research represents a significant step forward in the development of LMFR technology. SACOS-LMR, with its validated capability in both steady-state and transient analysis, stands as a sophisticated and reliable sub-channel analysis tool. It not only supports LMFR core design but also contributes to the broader global pursuit of sustainable and clean energy solutions in the nuclear energy landscape.

RELAP5 is one of the most commonly used programs for reactor thermal hydraulic analysis. Due to the early developing time, RELAP5 does not have a friendly graphical user interface and interactive interface, resulting in the lack of human-computer interaction ability. In this work, the visual interactive simulation platform VITARS was developed by Java Script language based on Node.js framework. The origin RELAP5 was reformed then integrated into VITARS, and a bidirectional data communication pipe was established between RELAP5 process and VITARS process. In VITARS, a modeling module was developed, in which all the components in RELAP5 were abstracted into different pictograms and users could complete graphical modular modeling and parameter input for RELAP5 conveniently by stitching these pictograms, thus the use threshold of RELAP5 could be reduced. Due to the data communication pipe, VITARS could send control instructions to RELAP5 for pause, run, snapshot, terminate etc. The calculation results in RELAP5 could be displayed in VITARS as dynamic data meter or dynamic time-data curve in real time, and could be saved in VITARS for future viewing and extraction. In addition, a new signal logic computation system was developed in VITARS, in which more than forty kinds of signal logic computing components were built-in such as logical gate, proportional-integral, time delay integration, and flip-flop. As a data processing center for VITARS, the new signal logic computation system could read the thermal-hydraulic calculation results from RELAP5, user’s operation instruction etc., these data could be processed then distributed to RELAP5 to replace the thermal hydraulic boundary in time dependent component, adjustable equipment parameters or origin control data in the next time step, and could also be distributed to the data display system for real-time display. Therefore, with VITARS, complex proportion integration differentiation control system could be built for RELAP5, and user could adjust valve opening, pump speed and other equipment parameters in real time just like the reactor operators. Moreover, VITARS reserves the interfaces for coupling with other reactor analysis programs. VITARS also has the ability for users to customize the running interface. User could draw any reactor systems as the display background and kinds of graphical components such as dynamic data meter, warning light, reactor shut-down switch could be added. So that VITARS could also be used as a lightweight simulator of nuclear power plants. Model of Ling’ao Nuclear Power Plant was developed and a steady-state simulation was performed in VITARS. The simulation results were compared with that from origin RELAP5 program, which indicates the calculation accuracy of VITARS. VITARS could not only improves the efficiency of RELAP5, but also enhances human-computer interaction capabilities, which could be helpful for reactor safety analysis and operator training work.

A functionalized cross-linked polyphosphazenes microsphere (Salen-PZN-Ni@Co-MOF) was fabricated by enveloping Salen-Ni-based polyphosphazenes (Salen-PZN-Ni) with a type of hybrid flame retardant (Co-MOF) to enhance the flame retardant, smoke suppression properties and mechanical properties of epoxy (EP) composites. Thermogravimetric analysis indicated that the incorporation of Salen-PZN-Ni@Co-MOF significantly enhanced the thermal stability of the EP composites. The existence of Salen-PZN-Ni@Co-MOF enhanced both the vertical burning rating and resulted in a higher limiting oxygen index. The addition of 5 wt% Salen-PZN-Ni@Co-MOF conspicuously improved the fire safety of EP, as evidenced by the results of the cone calorimeter. For instance, the peak heat release rate and total heat release rate of the EP composites were decreased by 25.3% and 44.97%, respectively. In addition, the incorporation of Salen-PZN-Ni@Co-MOF significantly inhibited the generation of toxic carbon monoxide and other volatile compounds. Furthermore, a synergistic effect between Salen-PZN-Ni and Co-MOF was observed. The proposed flame retardant mechanism of Salen-PZN-Ni@Co-MOF is attributed to the synergistic catalytic carbonization effect and the formation of thermally stable components. Consequently, enhanced fire safety in EP composites is achieved through the synergistic interaction among various components (nickel and Co-MOF) with polyphosphazene microspheres. Meanwhile, the excellent compatibility between Salen-PZN-Ni@Co-MOF and EP enhances the mechanical properties of EP composites. [ABSTRACT FROM AUTHOR]